Do you have to burn it to a USB/CD as the page suggests, or is does the tool give a way to upgrade in place without doing that?
Edit: can confirm crazysaem's experience. I did an in-place upgrade on a fully-patched 8.1 system and it worked flawlessly and relatively quickly (I kept my apps and settings). I'm not a heavy Windows user though.
You have the option to either create the USB/CD media or do an in-place upgrade. I did the in-place upgrade, which worked without problems for me. They also provide the option to either keep your apps and files or delete them. I chose to delete them, because I wanted a clean install.
Edit: can confirm crazysaem's experience. I did an in-place upgrade on a fully-patched 8.1 system and it worked flawlessly and relatively quickly (I kept my apps and settings). I'm not a heavy Windows user though.